@Eugenev24 

Hi All, good day!

Later, if you all have the same issue about failing to obtain the IP address, we might need your help to get more information for further analysis, and Thank you in advance.

Please email to our support team https://www.tp-link.com/en/support/contact-technical-support/#E-mail-Support  with the following answers and add forum ID 165452 unstable connection with error Fail to obtain the IP address;

1. What is the modem number of your range extender, RE450, or RE300, even something else? And how about the hardware version and firmware version?
2. May I know the model number of your main router?
3. How many devices are connected to the extender and what are they?
4. Did all the mobile devices connected to the range extender, have the same issue? And Did it happen to all the devices at the time? How about the dropping frequency?
5. If possible, please connect a wired device via cable to the range extender to see whether it could get an IP address or not？

And here are some suggestions for your reference:

1. Always update the firmware of  the router to be the latest one;
2. Move the extender a little bit closer to the router;
3. Change the channel and channel width about the main router, such as channel 11, channel width 20mhz for 2.4gzh; channel 48 and channel width 40mhz for 5ghz;

Thank you very much for your cooperation and support.